This invention concerns a riser pipe, hereinafter called merely riser, for use at great water depths, giving passage to transfer lines connecting a submerged structure such as a submerged oil well to a caisson of positive buoyancy.
It is known in the art to make use of risers for transferring the production of a submerged oil well.
According to a first embodiment of the prior art illustrated for example, by French patent application No. 2,344,442, a flexible line connects the submerged fluid source to a buoy anchored by means of several cables. The length of the line is greater than the distance between the buoy and the water bottom, so that the line is not stretched. According to another embodiment, illustrated by the French patent application No. 2,199,053, there is used at least one line stretched by means of at least one buoy to which it is connected, said buoy being either floating or submerged as illustrated in the French Pat. No. 2,303,702.
These risers can be used at water depths not in excess of 200 to 300 meters. Beyond these values, the movement of the buoy generates excessively high overtensions in the risers of the first type, whereas the dilatations of the line would result in unacceptable displacements of the buoy for the risers of the second type.
The riser according to the present invention avoids these disadvantages and, accordingly, can be used at great water depths reaching or even exceeding 3000 meters.